Heat exchanger with dimpled tube surfaces

ABSTRACT

A heat exchanger including a shell having an inner chamber defined by an inside wall surface, and a tube stack disposed within the inner chamber. The shell is formed of a single piece of material. The tube stack includes a plurality of flat elongated tubes arranged in a stack. Each of the tubes is formed of a single piece of material that is joined along a seam. A first fluid flow path is defined within the tubes. The tubes each include a plurality of projections projecting outwardly therefrom. The projections on adjacent tubes contact one another, thereby forming a second fluid flow path.

FIELD OF INVENTION

This invention relates generally to the field of heat exchangers and, more particularly, to heat exchangers that include a plurality of dimpled, one-piece tubes that are stacked within a surrounding shell.

BACKGROUND OF THE INVENTION

The present invention relates to heat exchangers that are generally configured comprising a number of internal fluid or gas passages disposed within a surrounding body. In an example embodiment, the internal passages are designed to accommodate passage of a particular fluid or gas in need of cooling, and the body is configured to accommodate passage of a particular cooling fluid or gas used to reduce the temperature of the fluid or gas in the internal passages by heat transfer through the structure of the internal passages. A specific example of such a heat exchanger is one referred to as a shell and tube exchanger, which can be used in such applications as exhaust gas cooling for internal combustion engines.

Referring to FIG. 1, a shell and tube heat exchanger 10 generally includes a tube bundle 12 formed from a plurality of individual tubes 14, i.e., internal passages, that are aligned together, positioned next to one another, and that have one or both openings at the tube ends 16 positioned adjacent one another. The tube bundle 12 is disposed within a surrounding shell 18. The shell is configured having an inlet 20 and outlet 22 to facilitate the passage of a fluid or gas into and out of the shell. Referring now to FIG. 2, in a single-pass shell and tube heat exchanger, the tube bundle 12 is configured so that the tube ends 16 pass through or are positioned adjacent respective ends 24 of the shell. In a dual or multi-pass shell and tube heat exchanger, the tube bundle is configured having one or more 180-degree bends at one of the tube ends to facilitate passage through the shell more than one time.

Referring back to FIG. 1, a tank or manifold 26 is attached to each end of the shell 18 and each serves to direct the flow of fluid or gas into and out of the tube bundle. Referring to FIG. 2 again, a header or tube plate 28 can be attached to the tube bundle adjacent one or more of the tube bundle ends 16 to form a connection or attachment point between the tubes in the tube bundle and/or between the tube bundle and a respective end of the shell. As best shown in FIG. 3, the header plate 28 connects the individual tubes 14 in the bundle together, connects the tube bundle to the shell 18, and provides a seal between the shell and the tube bundle so that fluid within the shell does not escape. The tank or manifold is typically attached by weld to the header plate to enable fluid tight transfer of fluid or gas from the tube bundle.

In a shell and tube heat exchanger configured for use in exhaust gas cooling, exhaust gas is passed through the tube bundle for cooling by use of a cooling medium such as water that is passed through the shell and thus placed into contact with the outside surfaces of the tube bundle tubes. Shell and tube heat exchangers are proven to be durable and easily manufactured, but heat transfer performance is typically poor. As a result, for high performance applications the heat exchanger has to be very large.

It is, therefore, desired that a heat exchanger be constructed in a manner that improves the heat transfer performance and that reduces the size of the heat exchanger, thereby providing a heat exchanger capable of handling relatively high performance applications in a relatively small size. It is further desired that such heat exchangers be constructed using materials and methods that are readily available to facilitate cost effective manufacturing and assembly of the same.

SUMMARY OF THE INVENTION

A heat exchanger constructed in accordance with principles of this invention generally comprises a shell having an inner chamber that is defined by an inside wall surface. In an example embodiment, the shell is formed having a one-piece configuration made from a single piece of material. A tube stack or core is disposed within the inner chamber of the shell and comprises a plurality of tubes that are arranged in a stack together configuration. The tubes that are used to form the tube stack are formed from a single piece of material. A first gas or fluid flow path of the heat exchanger is defined within the tubes. If desired, the tubes can includes a flow element disposed therein to create more than one gas fluid flow path within the tube.

The tubes are constructed to include a plurality of projections that extend outwardly from an outer surface of the tubes. The projections are arranged along an outside surface of the tubes such that the projections on adjacent tubes contact one another and form a second gas or fluid flow path of the heat exchanger across the outer surfaces of adjacent tubes. The projections may or may not be bonded or otherwise attached together. The projections can be positioned along the outside surface of the tubes to provide a second gas or fluid flow path that is not linear or that does not provide a straight-line passage of gas within the heat exchanger.

Heat exchangers constructed in this manner, comprising projections along the outside surface of the tubes in the tube stack, provide pressure containment, operating to lower the gas and coolant pressure stresses in the exchanger. Further, they operate to provide spacing between the tubes, allowing for the passage of a desired fluid or coolant therebetween. Further, the use of such projections provide turbulence within the second gas or fluid flow path to increase the heat transfer coefficient on the coolant side of the tubes. Finally, they operate to provide structural support among the number of tubes within the heat exchanger to eliminate vibration of the tubes relative to one another, thereby operating to help reduce vibration induced heat exchanger failures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood with reference to the following drawings wherein:

FIG. 1 is a perspective view of a prior art shell and tube heat exchanger;

FIG. 2 is a perspective view of the prior art heat exchanger of FIG. 1, illustrating placement of a tube bundle within a shell;

FIG. 3 is a perspective view of the prior art heat exchanger of FIGS. 1 and 2, illustrating the tube bundle as attached to the shell;

FIG. 4 is a perspective view of a heat exchanger of this invention illustrating the shell and a tube stack in an assembled state;

FIG. 5 is a cross-sectional view of the heat exchanger of FIG. 4 taken along line 5-5 of FIG. 4;

FIG. 6 is a perspective view of a tube taken from the tube stack, in accordance with the invention;

FIG. 7 is a cross-sectional end view of two tubes in the tube stack, in accordance with the invention; and

FIG. 8 is a perspective view of a header plate, in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to heat exchangers used for reducing the temperature of an entering gas or fluid stream. A particular application for the heat exchangers of this invention is with vehicles and, more particularly, is to cool an exhaust gas stream from an internal combustion engine. However, it will be readily understood by those skilled in the relevant technical field that the heat exchanger configurations of the present invention described herein can be used in a variety of different applications. Generally, the invention constructed in accordance with the principles of this invention, comprises a heat exchanger including a stack of elongated, dimpled, flattened tubes that are enclosed in a surrounding shell.

FIG. 4 illustrates a perspective view of a heat exchanger 30 of this invention, and FIG. 5 illustrates a sectional view of the heat exchanger taken along line 5-5 of FIG. 4. The heat exchanger 30 comprises a tube stack 31, formed from a plurality of elongated and flattened tubes 38 that are each arranged in a stack, which stack is disposed within the shell 32. A header plate 34 (also shown in FIG. 8) is positioned adjacent both ends of the tube stack 31, and operates to connect the tubes 38 together adjacent the tube ends, seals the tubes 38 from the coolant, and as better described below provides a structure for connecting the tube stack 31 to the shell 32.

In an example embodiment, the shell 32 is configured to surround the tube stack and includes a coolant inlet and a coolant outlet to facilitate passage of a desired cooling fluid or medium therethrough. The shell can be formed from suitable structural materials such as metals, metal alloys and the like having desired structural and mechanical properties enabling use in such a heat exchanger application. In a preferred embodiment, the shell is formed of a single piece of material. In a preferred embodiment, the shell 32 is made from a stainless steel material. The shell can be made by molding process or the like. In a preferred embodiment, the shell is made by hydroforming or end expanding a seam welded rectangular tube.

In an example embodiment, the shell 32 is configured having a geometry that both surrounds the tube stack and that facilitates a desired degree of coolant circulation therein to provide a desired degree of heat transfer contact with the tube stack. In the example embodiment illustrated in FIGS. 4 and 5, the shell is configured having a generally rectangular cross-sectional geometry, and includes an inlet end 32 a at one end of the shell, and an outlet end 32 b at an opposite end of the shell. As shown in FIG. 4, the outlet end 32 b includes a flange that is attached thereto for the purpose of connecting the heat exchanger to a further device or system element, e.g., a portion of an exhaust gas handling system.

As is shown in FIG. 5, the tube stack 31 comprises a plurality of individual tubes 38 that are arranged in combination with one another. In an example embodiment, the tubes are stacked on top of one another. As best shown in FIG. 6, each tube 38 in the tube is formed from a single sheet of material that has a pair of edges 38 a and 38 b that extend longitudinally along a length of the tube running between tube ends 39 and 41. In an example embodiment, tubes are formed by bending the sheet of metal into a desired configuration that will provide opposed tube outside surfaces to facilitate stacking and connection with adjacent tubes as better explained below. In a preferred embodiment, the tube is formed by bending the metal sheet about itself to provide central passage defined by a wall structure configuration that having a generally rectangular or flattened oval cross section.

During the process of forming the tube, the edges 38 a and 38 b are positioned adjacent or abutting one other, and are attached to each other to form a seam 38 c that runs lengthwise along the tube. In a preferred embodiment the tube will be formed in a high speed tube rolling mill (10-100 m/min speed). The tube edges 38 a and 38 b are attached to one another by bonding process such as by brazing, welding or the like, and in a preferred embodiment can be attached by TIG or high frequency welding, or can be attached without a welded joint by brazing together.

A feature of this invention is the formation of the tubes from a single sheet of material, thereby providing a tube having essentially a one-piece constriction. Such method of tube fabrication makes the tubes 38 easy to manufacture and durable for high performance applications, e.g., the single seam attachment operates to minimize any potential leak points in the tube to one. As illustrated in FIGS. 6 and 7, an example embodiment of the heat exchanger can include tubes 38 that include a flow element 40 disposed therein. The flow element 40 can be provided in the form of a corrugated member or the like that extends a partial or complete length of the tube. The flow element 40 can be referred to as a fin or a turbulator, and can form a further flow path 46 within the tube, operate to increase the gas or fluid contact surface area within the tube, and operate to increase flow turbulence therein, which can aid in cooling the fluid flowing through the tubes 38. Additionally, the fin or turbulator can function to add structural rigidity to the tube if desired.

As shown in FIGS. 6 and 7, the tubes 38 are configured each having an outside surface or surfaces 42 that includes a plurality of projections 43 or dimples extending outwardly therefrom. Preferably, the projections 43 are formed along a portion of the tube 38 defining one or more outside surfaces 42 by the process of stamping, embossing or the like. In an example embodiment, where the projections are provided in the form of dimples, the dimples can either be rolled or stamped into the material in the tube mill prior to the tube radii forming operation. In an example embodiment, the projections are formed on both opposed outside surfaces 42 of the tube that generally extend between the tube lengthwise edges (as best illustrated in FIG. 6). The projections can have a random or ordered repeating arrangement.

The projections can be configured having a number of different shapes, e.g., round, square, tapered, having constant, tapered or offsetting cross-sections. For example, the projections could be provided in the form of dimples having a short angled rib (30-45° angle), which when put next to an adjacent tube will form an X pattern with two opposing angled ribs. In an example embodiment, the projections are configured having a circular cross section and having a rounded outside surface shape. The projections can extend a predetermined distance from the tube outside surface, which distance can vary depending on a number of factors such as the type of coolant being passed through the shell, the desired flow rate or residence time for the coolant, and the like. In an example embodiment, the projections can extend a distance from the outer surface 42 in the range of from about 0.5 mm to 2 mm, and more preferably about 1 mm. In an example embodiment, wherein the tubes are sized having a length of from about 110 mm to 720 mm, and a width extending between the lengthwise edges of in the range of from about 40 mm to 120 mm, the projections are sized to extend a distance from the outer surface approximately 1 mm.

In the example embodiment illustrated in FIG. 6, the projections have an ordered arrangement that is provided in the form of repeating rows (extending widthwise between the lengthwise edges of the tubes) of 3 and 4 projections. As described below, this repeating arrangement of differently positioned, e.g., staggered, and numbered projections operates to provide a discontinuous coolant flow path between adjacent tubes within the tube stack. It is to be understood, however, that this arrangement of projections is but one example and that other arrangements of projections are understood to be within the scope of this invention. In an example embodiment, it is desired that the arrangement or pattern of projections be the same for the tubes so that the projections of adjacent tubes can register and contact one another when assembled in the tube stack.

With this arrangement, the projections 43 disposed along the outside surfaces of the tube operate in effectively increase the surface area of the tube to be cooled, and operate to increase the turbulation of the cooling fluid within the heat exchange to increase the heat transfer coefficient of the surface and avoid boiling of the coolant. Both of these features operates to improve heat transfer from the tubes and, thereby improve the cooling of the fluid or gas that is transferred therein and the heat transfer efficiency of the heat exchanger. In another embodiment, rather than being integrally formed from the material used to form the tube, the projections 43 can be provided in the form of separate elements, i.e., nonintegral elements, that are attached to the outside surface or surfaces 42 of the tubes 38.

As shown in FIG. 7, adjacent tubes 38 are preferably arranged and oriented with one another so that when they are placed in a stacked position, the projections 43 of adjacent tubes 38 make contact with one another. This arrangement of adjacent tubes within the stack having adjacent projections in contact with one another operates define a plurality of spaces or channels 47 between the outside surface of adjacent tubes to define and direct the passage of the coolant therethrough. As noted above, the projections can be oriented along the tube surface in a manner that gives rise to a plurality of coolant passages 47 that are configured to influence the passage of coolant through the tube stack in a manner that improves thermal transfer within the heat exchanger.

The projections 43 of the adjacent tubes can be brazed or welded together in the tube stack. Alternatively, the projections of the adjacent tubes can just be in contact with another without being bonded together. In an alternative embodiment, the projections on adjacent tubes can be arranged differently such that they do not correspond to one another, but instead contact the outside surface of the adjacent tube, thus forming a plurality of spaces between the tubes that also operates to form coolant passages between the tubes.

The projections 43 disposed along the tube surfaces provide a number of advantages. First, they provide pressure containment, operating to lower the gas and coolant pressure stresses in the exchanger 30. Second, they provide spacing between the tubes 38, allowing fluid (typically coolant) to flow therebetween. Third, they provide turbulence, increasing the heat transfer coefficient on the coolant side of the tubes 38. Fourth, they provide support among the number of tubes within the heat exchanger to eliminate vibration of the tubes relative to one another, thereby operating to help reduce vibration induced heat exchanger failures. Lastly, during manufacturing they provide compression force on the tubes 38 ensuring that all the tubes 38 and fins 40 achieve an adequate braze. As noted above, the projections 42 can be configured having a variety of different shapes including, but not limited to, round, square, tapered, offset crosses, frusto-conical and the like.

As shown in FIGS. 5 and 8, header plates 34 are disposed within the heat exchanger and are configured having inside surface features extend around respective opposed ends of the tube stack 31, and having an outside surface that is configured and sized to complement and fit within an inside wall surface of the shell 32. As best illustrated in FIG. 8, the header plate 34 is generally rectangular in shape and includes a number of openings 45 that are configured and sized to accept placement of end portions of the tubes within the tube stack therein.

The header plates 34 are attached to the outside surface of each end of the tube stack 31 during the brazing process. Once the tube stack 31 has been assembled and inserted into the shell 32, the header plates are attached to the inside wall surface of the shell by brazing, welding or the like. Bonding the header plates to the inside wall surface of the shell helps to provide a sealed coolant passage. It will be understood that the tube stack 31 is preferably dimensioned so that it fits tightly into the shell 32. In a preferred embodiment, this tight fit acts as a brazing fixture providing compression force on the tubes 38 to achieve the braze joints in the core stack. This tight fit also helps to prevent/control separation of the tubes caused by expansion during use.

The header plate 34 preferably includes a shoulder 48 that defines a transition between the main body 50 of the header plate 34 comprising the number of openings 45, and an axially projecting section 44. The header plate shoulder 48 and is sized and configured to provide a cooperative nesting fitment within a complementary surface feature of the shell inside wall surface when the tube stack 31 is placed within the shell. If desired, the header plates 34 can also be configured having a self-fixturing or registering means disposed along an outside surface for placing it in a particular position with respect to the shell during assembly and brazing.

Referring back to FIG. 4, after the tube stack 31 has been positioned within the shell 32 and fixedly connected into place as described above, a diffuser 52 is attached to the inlet end 32 a of the shell 32. The diffuser 52 also includes a flange 54 for connecting the heat exchanger 30 to another device or portion of the cooling system. For example, when placed into use to cool exhaust gas of an internal combustion engine, this flange can be connected to a fluid handling device receiving exhaust gas from the engine. The diffuser can be connected to the shell by conventional attachment methods, such as by welding, brazing or the like. It is to be understood that the use of a diffuser can be optional, and that heat exchanges constructed in accordance with principles of this invention may or may not include a diffuser depending on the particular end use application.

In general, the entire assembly is preferably made of metals and metal alloys, such as stainless steel or the like, and the assembly elements are brazed using a braze material that is compatible with the selected metal or metal allow, e.g., with a nickel-based braze material or the like when the selected material useful for making the heat exchanger elements is stainless steel.

The heat exchanger as constructed in accordance with the principles of this invention functions in the following manner. The desired fluid or gas to be cooled is directed into the heat exchanger via the inlet opening 32 a, through the diffuser 52 and into and through the plurality of tubes making up the tube stack. Within the tubes, the gas or fluid flows across the fins of the turbulator 40, and within the further defined channel or passage 46 therein.

Coolant enters the heat exchanger via a coolant inlet and is placed into contact with the tube shell. As noted above, and as shown in FIG. 7, the assembly of adjacent tubes 38 within the tube stack define the coolant flow paths 47 between and across the adjacent surfaces of the tubes. Thus, the overall coolant flow path within the heat exchanger is generally defined by the inside wall surface of the shell 32, the outside surface of the tubes 38, and the placement position and of projections 42 along the outside surface of the tubes.

The coolant operates to reduce the temperature of the gas or fluid being passed through the tube stack via thermal heat transfer and the cooled gas or fluid exits the heat exchanger via the outlet opening 32 b. Coolant that has passed through the tube stack exits the heat exchanger via a coolant outlet.

It is to be understood that the embodiments described above and illustrated are but examples of examples embodiments of heat exchangers as constructed according to principles of this invention, and that those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention. 

1. A heat exchanger comprising: a shell having an inner chamber defined by an inside wall surface; and a tube stack disposed within the inner chamber and comprising a plurality of tubes arranged in a stack, wherein the tubes are formed from a single piece of material, wherein a first gas or fluid flow path is defined within the tubes, wherein the tubes each include a plurality of projections extending outwardly from an outer surface, and wherein projections on each tube contact an adjacent tube so as to form a second gas or fluid flow path between and across the outer surfaces of adjacent tubes.
 2. The heat exchanger as recited in claim 1 wherein the projections on a first tube contact projections on an adjacent to so as the create a space between the tubes, the height of said space being approximately the combined height of the contacting projections.
 3. The heat exchanger as recited in claim 2 wherein the projections of adjacent tubes are bonded together.
 4. The heat exchanger as recited in claim 1 wherein the shell has a one-piece construction made from a single piece of material.
 5. The heat exchanger as recited in claim 1 wherein the projections are arranged along each tube outer surface such that the second fluid flow path is non linear.
 6. The heat exchanger as recited in claim 1 further comprising a flow element disposed within at least one of the tubes that creates more than one first gas or fluid flow path within the tube.
 7. The heat exchanger as recited in claim 1 wherein the projections extend a distance from the tube outer surface in the range of from about 0.5 mm to 2 mm.
 8. The heat exchanger as recited in claim 1 further comprising a header plate attached to the tubes and positioned adjacent an end of the tube stack, the header plate being interposed between the tube stack and the an inside wall surface of the shell.
 9. The heat exchanger as recited in claim 1 wherein the tubes are shaped having a rectangular cross section, and wherein the tubes include a single seam that extends lengthwise between opposed open tube ends.
 10. A method of making a heat exchanger comprising the steps of assembling a plurality of tubes into a stacked arrangement to form a tube stack, wherein each tube is one-piece construction formed from a single piece of material, and wherein each tube includes an outer surface that comprises a plurality of projections that extend outwardly therefrom, wherein the projections on each tube in the stack contact an adjacent tube so as to form a fluid flow passage between and along outside surfaces of adjacent tubes, and wherein the tubes are secured within the tube stack by a header plate at opposed tube ends; inserting the tube stack into a shell, wherein the header plate is interposed between the shell and assembly of tubes; and sealing one or more ends of the shell to encase the tube stack therein, and to form a leak tight seal between gas or fluid flowing through the tube stack, and gas or fluid flowing between the tube stack and the shell.
 11. The method as recited in to the claim 10 further comprising before the step of inserting, bonding the projections of adjacent tubes.
 12. The method as recited in claim 11 further comprising, forming the shell from a single piece of material to form a one-piece construction.
 13. The method as recited in claim 10 further comprising before the step of inserting, forming the projections in a pattern such that the gas or fluid flow passage is non linear.
 14. The method as recited in claim 10 further comprising before the step of inserting, forming the projections, wherein the projections extend a distance from the tube outer surface in the range of from about 0.5 mm to 2 mm.
 15. The method as recited in claim 10 further comprising, before the step of assembling, forming the tubes from a single piece of material that is joined together along a single lengthwise edge.
 16. The heat exchanger as recited in claim 10 wherein the projections on a first tube contact projections on an adjacent so that the height of the space created between the adjacent tubes is approximately the combined height of the contacting projections. 